Thermopile power supply in water heater control

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I recently bought a gas water heater and made a point of getting one
that didn't require external electrical power to operate.  

To my astonishment, it nonetheless came with what behaves like a digital
controller, complete with a green LED status light that must require close
to 3 volts to turn on.  

The electronics are operated from a standard Honeywell thermopile generator
producing 750 mV open circuit with a 3 ohm source impedance. I expected to
find an explanation of how it's done via a quick Web search, but have so
far come up with nothing very informative: Only that one can get MOSFET
transistors "programmed", evidently by something like charge trapping,
to have arbitrary gate threshold voltage, down to zero. That seems rather
exotic for a water heater 8-)

Can somebody point me to an application note explaining how this is done?  

Thanks for reading,

bob prohaska




Re: Thermopile power supply in water heater control
bob prohaska wrote:
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 ** It might use one of these, or similar.  

http://cds.linear.com/docs/en/design-note/dn428f.pdf

All fitted into a 2mm square, SMD package.  



.....  Phil  


Re: Thermopile power supply in water heater control
Phil Allison wrote:
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 ** Or this one, specially for thermopiles.  

 http://cds.linear.com/docs/en/datasheet/3108fc.pdf


.....   Phil  


Re: Thermopile power supply in water heater control
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That's plausible, it mentions Honeywell by name.

What search terms did you use? I tried thermopile in
various combinations and never came close....

Thank you!

bob prohaska


Re: Thermopile power supply in water heater control
bob prohaska wrote:
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 ** The first  LT device I linked came from " 700mV boost converter" and the LT3108 is mentioned at the top of the first LT page .  

 Couldn't have been easier.  

.....  Phil  


Re: Thermopile power supply in water heater control
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8-)
"boost converter" never occurred to me......

thanks,
bob

Re: Thermopile power supply in water heater control
bob prohaska wrote:
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** Shame on you - there simply had to be one of 'em in some form.  

 I didn't know specific thermopile input ones existed.  

 Using a 1:100 input tranny IS a neat idea.



....   Phil  

Re: Thermopile power supply in water heater control
On 04/18/2017 09:57 PM, bob prohaska wrote:
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I have one like that.  There's a battery in the control box.

Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
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Re: Thermopile power supply in water heater control
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Hmm, I hope not. Nothing said in the (very skimpy) instructions
about batteries, but there could be a battery. The entire heater is  
warranted only for six years, so a lithium coin cell as a backup
would have a long enough life.

Time will tell......

bob prohaska
  

Re: Thermopile power supply in water heater control
On Wed, 19 Apr 2017 01:57:47 +0000, bob prohaska wrote:

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I get 45mW from the thermopile -- that's enough to light up the LEDs in  
interior light, and have enough left over to run a thrifty microprocessor.

--  

Tim Wescott
Wescott Design Services
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Re: Thermopile power supply in water heater control
On Wed, 19 Apr 2017 01:57:47 +0000 (UTC), bob prohaska

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That sounds like the Honeywell Frankenstat. It is powered by the
thermocouple, probably with some sort of switching regulator voltage
booster.

They occasionally screw up, and there are Youtube videos about how to
prevent it, and how to reset them after they throw an error.

http://learnbyblogging.com/honeywell-water-heater-thermostat-woe-how-i-fixed-it/


--  

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement  

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Re: Thermopile power supply in water heater control
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Mine looks essentially the same, apart from color scheme. No battery, which
is good, but it sounds like reliability is an issue.

Once the warranty expires I'll likely have to become an expert.....

Thanks for writing,

bob prohaska


Re: Thermopile power supply in water heater control
On Wed, 19 Apr 2017 01:57:47 +0000 (UTC), bob prohaska

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Google "energy harvesting" and/or "Joule thief"
just for entertainment.

w.

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